Actuators are used in many different applications and particularly in manufacturing operations using machinery. Such actuators generally provide a reciprocal movement to a member such as a bellcrank mounted to a shaft, which shaft the bellcrank rotates under the influence of the actuator.
In lumber mills, for example, board retaining devices are used to restrain the cut boards in position on a table on which the boards are being moved by a conveyor. An actuator provides for the release of the restrained boards for further processing and such movement is performed periodically. As a bellcrank rotates under the influence of the actuator, the board retainer moves between two positions, the first position restraining the conveyed boards and the second position where the restrained boards are released. Many other applications use reciprocal movement of members and actuators are used to provide such reciprocal movement in many instances.
Heretofore, the bellcranks being rotated by the action of the actuator extended from a shaft and were fitted within a clevis which formed one end of a piston movable by a hydraulic or pneumatic cylinder. Air was pumped into the cylinder which would then extend or retract the piston. This rotated the bellcrank and the shaft to which the bellcrank was attached. The pneumatic cylinder was mounted for limited rotational movement on a base.
There are, however, numerous problems with present actuators and the operation of such actuators. First, the movement of the piston due to the ingress and egress of air in the pneumatic cylinder is not smooth. Rather, the piston quickly moves under the incoming influence of the air and stopping force is provided by contact between the piston and the cylinder when the end position of piston travel has been reached. This impact force at the end of piston travel results in wear and damage and early breakdown of components. Second, it is important that the shaft to which the bellcrank is mounted moves a predetermined amount in a fairly precise movement range. This is so because the position of the members controlled by the rotation of the shaft is determined by the movement of the bellcrank under the influence of the actuator. Thus, the tolerances between movement of the piston and the bellcrank are relatively close. Shock or impact loading as is obtained with the present actuator results in the tolerances being lost over time and these tolerances must be manually reset often. This results in inefficient and increased manpower requirements. Third, when the machinery is initially set up or if actuators are replaced, the tolerances must be manually reset. This setup is also time consuming and labor intensive.